The present invention relates to a fiber-reinforced rubber article and more particularly to a reinforcement embedded in a rubber article.
Since high tensile strength plessley, high elasticity, high dimensional stability, and high adhesive strength has been required for rubber in a belt, a tire, and a hose, a reinforcing cord constructed by fibers or a reinforcing canvas has been embedded in the rubber. Generally, cords of twisted yarns are used for the reinforcement. The cords are grouped into all-yarns-twisted cords, half-yarns-twisted cords, or lang lay. The all-yarns-twisted cords are the most popular for reinforcement for a rubber.
However, when the all-yarns-twisted cords are embedded in rubber as reinforcement, monofilaments rub each other at a sharp angle within the all-yarns-twisted cord. Accordingly, the yarn is abraded, broken, or decreased in strength from the rubbed part after a short period of usage. Therefore, the flex fatigue is lowered.
Japanese Patent Application Laying Open Gazette No. 59-19744 proposed a fiber-reinforced rubber, which reinforcement is constructed by half-yarns-twisted cords or lang lay to solve the above problem (flex fatigue).
However, rubber reinforced by half-yarns-twisted cords or lang lay is lowered in elongation and rate of tensile elasticity after the dipping process as compared with rubber reinforced by all-yarns-twisted cords. This results in lower dimensional stability.
Also, since the half-yarns-twisted cords or lang lay are twisted in only one direction, inversion and loosening of the cords is easily caused at an end. This makes the processing of the cord harder. Furthermore, fraying is easily caused in the place where the cord is cut during the processing of the cord.
When the half-yarns-twisted cords or lang lay are used as a reinforcement for an industrial belt, there exists a problem in that only one side of the belt is abraded soon, since the running belt inclines to one side. This inclination is caused by the twist direction of the cords, such as a half-yarns-twisted cord. On the other hand, the Japanese Patent Application Laying Open Gazette No. 56-103008 disclosed a conveyor belt, in which a reinforcement consists of half-yarns-twisted cords of S-twist and half-yarns-twisted cords of Z-twist alternately in order to prevent the uneven abrasion. However, in this case, two kinds of cords (both are half-yarns-twisted cords) are set in a parallel spiral in a belt structure, a total of four places are cut in every pair of two cords, on the right and left sides of the belt. Therefore, the maintainability of the tensile strength is lowered.
On the other hand, a braided cord has been used for various purposes. Particularly, a cylindrically braided cord is superior in flex fatigue due to its constructional characteristics, and it is also superior to a twisted cord in dimensional stability. Therefore, the cylindrically braided cord will improve both the flex fatigue and dimensional stability if ti si used for a reinforcement for a rubber. Further, cylindrically braided cords are superior in processing, since no loosening by inversion at an end of the cord, such as in half-yarns-twisted cords or lang lay, is caused. Therefore, a cut end is not frayed in processing. Furthermore since cylindrically braided cords don't possess the twisted direct on like half-yarns-twisted cords, the industrial belt maintains stable running without inclination and consequently uneven abrasion can be prevented.
However, the above cylindrically braided cord may possess a relatively large hollow inside of the cord. The size of the hollow depends on the number of yarns used for forming the cord. In case a large hollow is formed, the cord becomes flat when it stretches. Thus, the cord still doesn't satisfy the dimensional stability requirement, even though it is better than the twisted cord.